Ye Shuyang, Foster Scott M, Pollit Adam A, Cheng Susan, Seferos Dwight S
Department of Chemistry , University of Toronto , 80 St. George St. , Toronto , Ontario M5S 3H6 , Canada . Email:
Department of Chemical Engineering and Applied Chemistry , University of Toronto , 200 College Street , Toronto , Ontario M5S 3E5 , Canada.
Chem Sci. 2018 Dec 19;10(7):2075-2080. doi: 10.1039/c8sc04808h. eCollection 2019 Feb 21.
Catalyst transfer polycondensation is the only method to prepare π-conjugated polymers in a chain-growth manner, yet several aspects that underlie this polymerization are not fully understood. Here, we investigate the nickel-catalyzed polymerization mechanisms of a series of thiophene monomers bearing different halogen functionalities (Cl, Br, I). We have discovered the significant role that halogens and magnesium salts play in this polymerization. More specifically, the catalyst resting state changes depending on the type of halogenated monomer. For chlorinated monomers a mixture of Ni(ii)-dithienyl and dissociated Ni(phosphine) complexes are the resting states, which results in uncontrolled polymerization. For brominated monomers, a Ni(ii)-dithienyl complex is the resting state, which leads to controlled polymerization. For iodinated monomers, a Ni(ii)-thienyl iodide complex is the resting state, and notable inhibition by magnesium salt by-products is observed. The catalyst resting state changes to a Ni(ii)-dithienyl complex when a turbo Grignard reagent (-PrMgCl·LiCl) is used. These findings are used to guide the design of a new monomer, 2-bromo-3-(2-ethylhexyl)-5-iodotellurophene, which enables the first controlled polymerization of a tellurophene monomer containing a sterically encumbered 2-ethylhexyl side chain. These insights are crucial for deepening the mechanistic understanding of Kumada cross coupling reactions and the controlled synthesis of π-conjugated polymers.
催化转移缩聚是唯一一种以链增长方式制备π共轭聚合物的方法，然而这种聚合反应背后的几个方面尚未得到充分理解。在这里，我们研究了一系列带有不同卤素官能团（Cl、Br、I）的噻吩单体的镍催化聚合机理。我们发现了卤素和镁盐在这种聚合反应中所起的重要作用。更具体地说，催化剂的静止状态会根据卤化单体的类型而变化。对于氯化单体，Ni(ii)-二噻吩基和离解的Ni(膦)配合物的混合物是静止状态，这导致聚合反应不受控制。对于溴化单体，Ni(ii)-二噻吩基配合物是静止状态，这导致可控聚合。对于碘化单体，Ni(ii)-噻吩基碘配合物是静止状态，并且观察到镁盐副产物有明显的抑制作用。当使用Turbo格氏试剂（-PrMgCl·LiCl）时，催化剂的静止状态变为Ni(ii)-二噻吩基配合物。这些发现被用于指导一种新单体2-溴-3-(2-乙基己基)-5-碘碲吩的设计，该单体实现了含空间位阻2-乙基己基侧链的碲吩单体的首次可控聚合。这些见解对于深化对熊田交叉偶联反应机理的理解以及π共轭聚合物的可控合成至关重要。
